To satisfy ever-increasing demands for wireless data traffic, wireless communication systems have been developed to support higher data rates. For example, technological development for wireless communication systems seeks to improve spectral efficiency on the basis of communication techniques such as Orthogonal Frequency Division Multiple Access (OFDMA) and Multiple Input Multiple Output (MIMO).
However, with ever-increasing demands for smartphones and tablet computers, the number of application programs generating a large amount of data traffic has rapidly increased, causing an explosive increase in demand for data traffic. Hence, improving spectral efficiency alone may be insufficient to meet such explosive demands for wireless data traffic.
As a means to overcome the above problem, wireless communication systems using the millimeter wave (mmWave) band have attracted much attention.
Wireless communication using the mmWave band may suffer from high propagation loss such as path loss and reflection loss owing to frequency characteristics of the mmWave band. Such high propagation loss causes a wireless communication system using the mmWave band to have a short range, reducing service coverage.
A wireless communication system using the mmWave band may adopt a beamforming technology to reduce signal path loss and increase the signal propagation distance, expanding service coverage.
Such a wireless communication system using beamforming may optimize the performance index such as Signal to Noise Ratio (SNR) by maximizing the beamforming gain. However, optimization of performance requires channel information, entailing a process of transmission of a reference signal (RS), measurement of a channel, and feedback of channel information or effective channel information. Particularly for a wireless communication system using bean forming based on multiple transmit antennas, considering overhead and complexity of per-antenna reference signal transmission, it is possible utilize reference signals corresponding to preset beams sent by multiple antennas. Here, the number of beams for reference signal transmission may be influenced by beamforming parameters (such as the number of array antennas, the number of antenna elements in an array antenna, and the number of RF (radio frequency) chains), and other implementation parameters viewed from system operational perspective such as the number of beams used to cover cells/sectors and beamforming gains).